Convergence of synaptic influences of contralateral somatic afferents on interneurons in segmental inhibitory pathways to motoneurons

Convergence of contralateral somatic afferent synaptic influences on segmental inhibitory neurons was investigated by intracellular recording of postsynaptic potentials of -motoneurons in experiments on cats. Excitatory synaptic influences of afferents of the contralateral flexor reflex were shown to converge on interneurons of both segmental inhibitory systems studied: afferents of flexor reflex and group Ia muscle afferents. Interneurons of inhibitory systems are exposed not only to excitatory but also to inhibitory contralateral influences. Contralateral inhibitory PSPs of montoneurons are produced through ipsilateral inhibitory systems; a leading role is played by inhibitory neurons of the flexor reflex system of afferents. Inhibitory neurons of the Ia system as a rule do not make an important contribution to generation of contralateral IPSPs.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 5, No. 5, pp. 476–484, September–October, 1973.     

Synaptic processes evoked by intracortical microstimulation in lumbar motoneurons of rats

Experiments with intracortical microstimulation and intracellular recording from motoneurons of the rat hind limb showed that synaptic effects due to activation of pyramidal neurons of the motor cortex and transmitted along the pyramidal tract are exclusively polysynaptic in character. Mainly excitatory effects were found in motoneurons of flexors and extensors, and of distal and proximal muscles. The minimal intensity of intracortical stimulation required for synaptic excitation of -motoneurons is 5–10 µA. Low-threshold synaptic effects in lumbar motoneurons and movements of the hind limbs are evoked from the same zones.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 5, No. 2, pp. 174–180, March–April, 1973.     

Monosynaptic control of spinal motoneurons from different levels of the brain

In experiments on cats and monkeys it is established that reticulo-, rubro-, and corticomotoneuronal influences are characterized by a number of common features: 1) they are produced by fast conducting fibers of the descending tracts; 2) they do not attain the critical level needed for AP generation; and 3) they are caused by implication of synapses that are predominantly located on dendrites of the motoneurons. Results of experiments carried out on lampreys and rats indicate that reticulo-motoneuronal monosynaptic projections emerge already at the earliest stages of vertebrate evolution and retain their significance in mammals. The data of research on supraspinal influences during ontogenesis indicate early development of descending stem projections. This enables us to regard cerebro-motoneuronal monosynaptic connections as an important component of supraspinal control of motoneurons, a component whose functional role is in large measure determined by interaction with other synaptic inputs of the motoneuron.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 2, pp. 203–215, March–April, 1970.     

Influence of forelimb afferents on the activity of lumbar spinal-cord motoneurons

Experiments were conducted on anesthetized cats with microelectrode recording to study the synaptic responses that develop in the lumbar motoneurons on stimulation of the afferent fibers of groups II and III in the nerves of the ipsilateral and contralateral forelegs. Stimulation of these afferents evoked predominantly inhibitory postsynaptic potentials (IPSP) in the extensor motoneurons and excitatory postsynaptic potentials (EPSP) in the flexor motoneurons. A basically inhibitory change in the rhythmic background activity developed under the influence of descending impulsation. The duration of the total inhibition of "spontaneous" motoneuron activity corresponded to the duration of the inhibitory influences exerted by the forelimb flexor-reflex afferents (FRA) on the interneurons. The interaction of the descending and segmental PSP resulted in inhibition and facilitation of the segmental responses in the motoneurons. The ultimate result of this interaction was determined by the shifts in the membrane potential of the motoneuron and by the effects created in the interneurons.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 3, No. 1, pp. 58–67, January–February, 1971.     

Rubrospinal synaptic influences on the lumbar motoneurons of the rat

Intracellular recording was employed in experiments on rats with the nervous system intact and after acute pyramidotomy to study the postsynaptic effects produced in the lumbar motoneurons on stimulation of the nucleus ruber. Stimulation of this nucleus with single stimuli and with a short series of stimuli caused excitatory and inhibitory postsynaptic potentials (EPSP and IPSP) to develop in the motoneurons. Most of the EPSP recorded were disynaptic, but response development involved a monosynaptic segmental delay in five of the 124 cells that exhibited EPSP. A capacity for high-frequency potentiation was a characteristic feature of the disynaptic excitatory and inhibitory effects. Transmembrane polarization of the motoneurons had a marked influence on the amplitude of the disynaptic EPSP and IPSP. The properties of the disynaptic rubrospinal influences were similar to those described for the cat.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 3, No. 3, pp. 266–273, May–June, 1971.     

Effect of the tendon reflex on motoneurons of the antagonist muscle in man

The knee jerk was elicited during regular firing of relatively low-threshold motor units of the biceps femoris muscle (during weak voluntary contraction). Besides the reflex response of the rectus femoris muscle, synchronous discharges of motor units of the biceps femoris muscle and activation of new motor units also were observed. Poststimulus histograms and statistical analysis of interspike intervals of motor units of the biceps femoris muscle revealed well-marked excitatory influences synchronous with the reflex response of the rectus femoris. This result can be explained by the presence of excitatory inputs of Ia afferents on motoneurons of the antagonist muscle. In the knee jerk, excitation of motoneurons of the antagonist was followed by later inhibitory influences which evidently correspond to the "silent period" of motoneurons of the agonist muscle during the elicitation of its tendon reflex.Institute for Problems of Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 8, No. 6, pp. 624–632, November–December, 1976.     

Synaptic effects evoked in motoneurons by stimulation of single propriospinal neurons

Experiments on cats with simultaneous extracellular recording, stimulation of single propriospinal neurons, and intracellular recording of unitary postsynaptic potentials from motoneurons, followed by computer averaging showed that direct stimulation of individual propriospinal cells receiving mono- and disynaptic influences from the medial reticular formation can evoke monosynaptic EPSPs and IPSPs in lower lumbar motoneurons. The amplitude of these EPSPs was 49.6±6.0 and of the IPSPs 28.9±2.9 µV and their synaptic delay was 0.34±0.05 msec. The same propriospinal neuron of the ventral horn of the upper lumbar segments may be connected with several motoneurons of the hind limb muscles.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 9, No. 3, pp. 300–306, May–June, 1977.     

Effects of the γ-aminobutyric acid antagonist disulfotetraazaadamantane on evoked neuronal response in hippocampal slices

The effects were investigated of disulfotetraazaadamantane (DSTA), a blocker of -aminobutyric acid, on summated potentials in field CA 1 of the mouse hippocampus arising in response to electrical stimulation of Shaffer's collateral. At a concentration of 5·10^–6–10^–5 M, DSTA led to a considerable increase in the amplitude of the main population spike (PS) and the onset of additional PS. The effects induced by DSTA resembled those observed following picrotoxin application, which it exceeded two- to threefold in intensity, however. Findings are reviewed from the standpoint of the effects exerted by the test substance on synaptic processes in the hippocampus in vitro.Institute of Physiologically Active Substances, Academy of Sciences of the USSR, Chernogolovka, Moscow Oblast. Institute of Brain Research, National Scientific Mental Health Center, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 21, No. 1, pp. 66–70, January–February, 1989.     

Morphological bases of interaction between motoneurons in spinal cord isolated from young rats using HRP techniques

The structure of connections between lumbar motoneurons was investigated in preparations of spinal cord isolated from young rats. This involved applying horseradish peroxidase to the ventral root and intracellular injection of the same enzyme into motoneurons. The possibility of dendro-dendritic, dendro-somatic, and somato-somatic contacts between motoneurons was shown up in light mocroscopy studies. Recurrent collaterals of motor axons were revealed and they are though to form contacts with dendrites and perikarya of the motoneurons. The findings obtained from morphological experiments are discussed in the light of data from electrophysiological analysis of motoneuronal postsynaptic potentials produced by ventral root stimulation.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 20, No. 3, pp. 340–350, May–June, 1988.     

Changes in distribution of synaptic vesicles in endings of cones during electrical stimulation of the retina

Conditions (hypoxia) were chosen under which, judging from the reduction in the responses of the horizontal cells to electrical stimulation of the retina, mediator is exhausted in the presynaptic endings of the photoreceptors. Under these circumstances a number of "small" synaptic vesicles were shown to be reduced in those parts of the cones which are in direct contact with presynaptic membranes. No significant changes were found in the total number of "small" vesicles in the cone endings.Institute for Problems of Information Transmission, Academy of Sciences of the USSR, Moscow. Institute of Biological Physics, Academy of Sciences of the USSR, Pushchino-on-Oka. Translated from Neirofiziologiya, Vol. 8, No. 6, pp. 620–623, November–December, 1976.     

Investigation of the mechanism of temperature sensitivity of the electroreceptors of ampullae of lorenzini

In experiments on Black Sea skates (Raja clavata), the potential of the receptor epithelium of the ampullae of Lorenzini and spike activity of single nerve fibers connected to them were investigated during electrical and temperature stimulation. Usually the potential within the canal was between 0 and –2 mV, and the input resistance of the ampulla 250–400 k. Heating of the region of the receptor epithelium was accompanied by a negative wave of potential, an increase in input resistance, and inhibition of spike activity. With worsening of the animal's condition the transepithelial potential became positive (up to +10 mV) but the input resistance of the ampulla during stimulation with a positive current was nonlinear in some cases: a regenerative spike of positive polarity appeared in the channel. During heating, the spike response was sometimes reversed in sign. It is suggested that fluctuations of the transepithelial potential and spike responses to temperature stimulation reflect changes in the potential difference on the basal membrane of the receptor cells, which is described by a relationship of the Nernst's or Goldman's equation type.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. I. M. Sechenov, Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Pacific Institute of Oceanology, Far Eastern Scientific Center, Academy of Sciences of the USSR, Vladivostok. Translated from Neirofiziologiya, Vol. 12, No. 1, pp. 67–74, January–February, 1980.     

Motoneuronal interaction in spinal cord isolated from infant rats

Intracellular investigations into interaction between lumbar motoneurons were made during ventral root stimulation in spinal cord isolated from 9 to 14-day-old rats and horseradish peroxidase injection. It was found that electronic interaction is brought about by contacts between a moderate number of adjacent motoneurons and does not lead to generation of action potentials. A potential chemical (excitatory) as well as electronic interaction between motoneurons was discovered, probably occurring via recurrent motor axon collaterals. It was shown that the way in which one motoneuron is influenced by others may be a factor of its functional pattern.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 20, No. 2, pp. 243–250, March–April, 1988.     

Potentials of spinal motoneurons in cats with experimental tetanus

Potentials of motoneurons of the lower segments of the spinal cord were recorded with the aid of intracellular microelectrodes in experiments on cats with induced tetanus produced by injection of tetanus toxin (1500–2000 mouse LD₅₀) into the extensor muscles of the left shin. Neither afferent volleys of impulses in cutaneous and muscle nerves, nor antidromic volleys in the corresponding ventral roots, produced IPSPs in motoneurons of the extremity into which toxin was injected. The form both of antidromic peak potentials and of monosynaptic EPSPs in motoneurons in which IPSPs were blocked by tetanus toxin did not differ from the form of corresponding potentials of motoneurons in normal cats. The values of threshold depolarization for peak discharges during synaptic and direct stimulation were equal in tetanus and control motoneurons. Resistance and time constant values of the membrane in "tetanus" motoneurons did not differ from the corresponding values for "control" motoneurons.N. I. Pirogov Second Medical Institute, Moscow. Translated from Neirofiziologiya, Vol. 1, No. 1, pp. 25–34, July–August, 1969.     

Parameters of a model of transmitter depletion in synapses of identified snail neurons

Elementary EPSPs arising in two different identified neurons of the parietal ganglion ofHelix pomatia were recorded after stimulation of the identified triggering neuron. Repetitive stimulation (0.1–1.5 Hz) led to low-frequency depression of EPSPs. By the use of known and modified models of transmitter depletion parameters characterizing storage, mobilization, breakdown, and liberation of transmitter were determined. The fraction of available pool (F) released in two different synapses of the same trigger neuron did not differ significantly. The available pool of transmitter (C) and the demobilization constant ( ) in synapses on the RPa3 neuron were 2–3 times higher, and mobilization (M) was 10 times higher than on the LPa2 neuron. Predictions of the depletion model showed deviations from the experimental data. A method of calculating consistently whatever law of change of F was adopted was devised. Absence of correlation between parameters F and C of the depletion model and binomial parameters p and n, calculated on the basis of the quantal hypothesis of synaptic transmission shows that this hypothesis and the transmitter depletion model describe different synaptic mechanisms.Brain Institute, Academy of Medical Sciences of the USSR, Moscow. Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 13, No. 1, pp. 88–97, January–February, 1981.     

A comparative study of the activity of motoneuron groups of intercostal muscles in cat

The activity of inspiratory and expiratory motor units (MU) has been studied. The statistical data indicate that the recruitment of expiratory motoneurons is slower and more uniform than the recruitment of the inspiratory motoneurons. Most of the expiratory motoneurons showed inhibition shortly before the start of the inspiratory phase. Data are given on other characteristics of the activity and segmental location of both groups of motoneurons. It is postulated that the changes in the MU activity at the beginning and the end of the respiratory period and the coincidence in the extremal activity values of the antagonistic groups are attributable to supraspinal influences.Information Transmission Problems Institute, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 2, No. 3, pp. 289–295, May–June, 1970.     

Action potentials of masseter motoneurons evoked by stimulation of low-threshold infraorbital nerve afferents in cats

In cats anesthetized with chloralose and pentobarbital stimulation of the infraorbital nerve by a volley of 3 or 4 stimuli 1.2 times stronger than the threshold for excitation of A-fibers caused the generation of action potentials in motoneurons of the masseter muscle if the frequency of stimuli in the volley exceeded 300/sec. Paired stimuli with a strength of 2.0 thresholds, and with an interval of 1.3–4.0 msec between stimuli, led to generation of an action potential by the motoneurons. If the interval exceeded 4 msec stimulation with a strength of 1.2–2.0 thresholds caused biphasic facilitation of the second EPSP with a facilitation factor of between 0.2 and 1.0. The small number of stimuli, combined with their high frequency in the volley, required for action potential generation by masseter motoneurons suggests that they are due to activation of A-fibers of the infraorbital nerve connected with fast-adapted receptors of the vibrissae.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 4 pp. 385–389, July–August, 1978.     

Effect of noradrenalin and serotonin on spontaneous unit activity in hippocampal area CA3 in vitro

The effect of noradrenalin and serotonin on spontaneous unit activity in hippocampal slices (area CA₃)in vitro was studied by the addition of mediators to the incubation medium. Both drugs were found to have both an inhibitory (32 and 49%, respectively) and an activating (52 and 35%, respectively) action. The effect of noradrenalin correlated with the type of spontaneous unit activity. Mainly cells without spontaneous discharges or with single irregular discharges were activated Cells with "complex discharges" were inhibited. Unlike the effect of serotonin, the activating action of noradrenalin was stimulated by the agonist phenylephrine and inhibited by the -adrenoblocker phentolamine. The action of the monoamines persisted in medium with an increased Mg⁺⁺ concentration.Institute of Biological Physics, Academy of Sciences of the USSR, Pushchino-on-Oka. Translated from Neirofiziologiya, Vol. 13, No. 5, pp. 482–490, September–October, 1981.     

Role of the adenylate cyclase system in cholinergic modulation of synaptic transmission in the hippocampus

Involvement of the adenylate cyclase system in cholinergic modulation of synaptic transmission was investigated in area CA1 in rat hippocampal slices. Microiontophoretic application of acetylcholine as well as addition of carbachol to the superfusate or of tolbutamide (a cAMP-dependent protein kinase inhibitor) depressed transmission at synapses formed by Schaffer collaterals and commissural fibers with dendrites of pyramidal cells belonging to hippocampal area CA1. Both numbers of free quanta of neurotransmitter and the likelihood of transmitter release decreased following carbachol action. Atropine suppressed the inhibitory action of carbachol on synaptic transmission. Dibutyryl cAMP and forskolin increased the amplitude of synaptic potentials and suppressed, either partially or in full, the inhibitory effects of cholinomimetics on synaptic potentials. It was concluded that cholinomimetics and activators of the adenylate cyclase system exert opposing effects on neurotransmission at synapses formed between Schaffer collaterals/commissural fibers and dendrites of pyramidal neurons belonging to hippocampal area CA1.Institute of Biophysics, Academy of Sciences of the USSR, Pushchino. Translated from Neirofiziologiya, Vol. 21, No. 4, pp. 435–442, July–August, 1989.     

Characteristics of interaction between central neurons and abdominal stretch receptors in the crayfish

Spontaneous activity of slow- and fast-adapted abdominal stretch receptor (SAR and FAR) of the crayfish and their activity evoked by adequate stimulation were investigated in the presence of efferent regulation. Activity of the receptors was shown to be under effective inhibitory control of two central neurons, principal and accessory; activity of these neurons, in turn, is determined by the current receptor activity. The closest interaction is found between SAR and the principal inhibitory neuron. Two types of efferent regulatory action of this neuron were discovered: grouped and continuous. Its powerful discharges (up to 361 spikes) arising in response to only one SAR afferent impulse are described. The character of synaptic connections between the peripheral and central neurons is discussed.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Institute of Zoology, Academy of Sciences of the Moldavian SSR, Kishinev. Translated from Neirofiziologiya, Vol. 4, No. 3, pp. 317–327, May–June, 1972.     

Response of human motor units to spinal and supraspinal inhibition

High-selectivity surface electrodes were used to record the activity of single motor units of the human flexor pollicis brevis muscle and their involvement in the "silent period" and the inhibitory phase of the startle response was compared. In both these situations the degree of inhibition was greater for motor units whose action potential had a smaller amplitude. In cases of spinal inhibition, an independent direct relationship also was discovered between the intensity of the inhibitory response and the mean duration of the prestimulus interspike interval, which was completely absent during supraspinal inhibition. Correlation between the parameters of the inhibitory response of the single motor unit to influences of both types was significantly weaker than correlation between the effects of the spinal rebound phenomenon after both responses. The results suggest that involvement of spinal motoneurons in the inhibitory response is determined by interaction between several relatively independent factors.Institute of Problems of Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 5, No. 3, pp. 298–306, May–June, 1973.